Justification:
The cause of the population reduction in this species (commercial whaling) is reversible, understood, and is not currently in operation. For this reason, the species is assessed under criterion A1, not under A2, A3 or A4. Physeter macrocephalus is globally widespread (thus not qualifying as threatened under criterion B), and does not have a global population that warrants listing under criteria C-D. Empirical trend data for this species globally are unavailable. However, commercial whaling at a large scale for this species in the North Pacific and Antarctic within the last three generations (82 years) certainly resulted in a global decline during this period. Commercial whaling for this species has ceased and therefore this population is evaluated under the A1 criterion rather than under the A2-4 criteria. A peer-reviewed publication (Whitehead 2002) provides a model-based estimate of global trend that can be used to evaluate the population under the A1 criterion. The results from that study gave a 6% probability for Endangered, a 54% probability of meeting the Vulnerable category, and a 40% probability of falling into the Near Threatened category. The results suggest little chance that the population would meet the criteria for Endangered or for Least Concern. There is credible and realistic evidence for either the Vulnerable or Near Threatened category. Given that the results give greater probability for at least the Vulnerable category (60%), and that this is the more precautionary category, the species is classified as Vulnerable.

The Sperm Whale has a large geographic range (Rice 1989). It can be seen in nearly all marine regions, from the equator to high latitudes, but is generally found in continental slope or deeper water. The distribution extends to many enclosed or partially-enclosed seas, such as the Mediterranean Sea, Sea of Okhotsk, Gulf of California, and Gulf of Mexico.

The only recent quantitative analysis of sperm whale population trends (Whitehead 2002; Fig. 1 in supplementary material, which constitutes an integral part of this assessment) suggests that a pre-whaling global population of about 1,100,000 had been reduced by about 29% by 1880 through “open-boat” whaling, and then to approximately 360,000 (67% reduction from initial) by the 1990s through modern whaling, although much uncertainty is associated with all these estimates (Fig. 1 in supplementary material). There is no direct evidence that any part of the population has increased since the end of large-scale whaling in about 1980, although for most areas there is also no direct evidence that they have not. In some areas there is concern that populations are continuing to decline (see below).

The species has a huge geographic range (Rice 1989) and a global population size in the 100,000's (Whitehead 2002; Fig 1). Although there is considerable uncertainty about sperm whale population parameters and levels of exploitation, Whitehead (2002) estimated historical trajectories of sperm whale abundance incorporating many, but not all, sources of uncertainty (Fig. 1 in supplementary material). That model was modified slightly (to produce an endpoint in 2003) and run to estimate the decline in global sperm whale population size between 1921 and 2003 (i.e. over approximately 3 generations; 82yr; see below for estimation of generation time) (H. Whitehead pers. comm.). As sperm whale population size seems to have changed rather little between about 1910-1930 (Whitehead 2002; Fig. 1 in supplementary material), the calculations are probably quite robust with reference to the estimated generation time. Using the “best” estimates of the model parameters (as in Whitehead 2002), the population in 2003 would have been 44% of that in 1921. Of 1,000 runs using model parameters randomly selected from within reasonable ranges (as in Whitehead 2002), 6% gave populations in 2003 of <30% of that in 1922, 54% gave a 2003 population between 30-50% of that in 1992, and 40% suggested depletion levels of less than 50% over this time.

Arguments can be made that the model results are overly optimistic or overly pessimistic. Factors that would contribute to making the results overly optimistic that are not accounted for in the model include not accounting for under-reporting of illegal Soviet catches in the North Pacific and Antarctica and under-reporting of Japanese catches in the North Pacific (Kasuya and Brownell 2001), other continuing threats (described below), and factors such as continuing effects of social disruption from whaling that might inhibit recovery (consistent with an apparent lack of recovery in many areas). Factors that would contribute to making the results overly pessimistic include the assumption of a relatively low rate of increase in the model and the extrapolation of a relatively high estimate of g(0) (the proportion of whales detected on the trackline) from a single study to the global population. The direction of the effect of other uncertainties in model inputs, including the effects of sex-biased catches, is not certain. Despite these uncertainties, the Whitehead model provides the best available scientific evidence upon which to base this assessment. To reduce these uncertainties, future analyses would need to address the concerns identified above.

Efforts to assess the conservation status of sperm whales and the impact of historical whaling on contemporary structure are compromised by the absence of a good model of sperm whale population structure; pooling data may obscure distinct geographic patterns. While Sperm Whales are known to show long distance movements (Ivashin and Rovnin 1967; Mitchell 1975) and low genetic differentiation among ocean basins, several lines of evidence suggest that sperm whales past and present, have significant geographic structure. Analyses based on historical and contemporary data from tagging records (Rice 1974; Kasuya and Miyashita 1988), blood types (Fujino 1963), catch distributions, sighting patterns, size composition, lack of recovery from exploitation (Japan), timing of pregnancy (Best et al.1984), photo-identification (Whitehead 2003), genetics (Drouot 2004; Mesnick et al. 1999), cultural markers (Rendell and Whitehead 2003) and combinations thereof (Bannister and Mitchell 1980; Kasuya and Miyashita 1988) suggest evidence for structure in many regions. Over the past decade, several authors have investigated population structure in female Sperm Whales using sequence variation within the mitochondrial control region DNA (mtDNA) and/or polymorphic nuclear loci (microsatellites). In general, results tend to find low genetic differentiation among ocean basins and little evidence of subdivision within ocean basins, with the exception of some isolated basins such as the Mediterranean and Gulf of Mexico (Lyrholm et al. 1999; Mesnick et al. 1999; Drouot et al. 2004). However, factors such as low sample sizes, low mtDNA haplotypic diversity and social structure alone and together reduce the power to detect population structure. In addition, it is clear that biologically discrete populations of odontocetes can occur independently of strong geographic or oceanographic features. Alternative, non-geographic based hypotheses of population structure, such as dialect and differences in diet such as are found in Killer Whales, have not been thoroughly examined. For example, Rendell and Whitehead (2003) suggest that female populations seem to be culturally structured within oceans by “coda” vocalizations and may be genetically distinct (Rendell and Whitehead 2005, Rendell et al. 2005).

The habitat of the Sperm Whale is the open sea. More specifically, Sperm Whales can be found in almost all marine waters deeper than 1,000 m that are not covered by ice, except in the Black Sea and possibly the Red Sea (Rice 1989; Whitehead 2003). In some areas, particularly in the western North Atlantic, sperm whales, especially males, can occur in shallower waters (e.g., Scott and Sadove 1997). Females and young are usually restricted to waters at latitudes lower than about 40-50º and to areas where sea surface temperatures are greater than about 15ºC (Rice 1989). Sperm Whales are generally more numerous in areas of relatively high primary productivity (Jaquet et al. 1996), although there are some exceptions, such as the Sargasso Sea and the central North Pacific gyre (Barlow and Taylor 2005).

The Sperm Whale is an animal of extremes in size (up to 18 m), sexual dimorphism (mature males have three times the mass of mature females), ecological imprint (sperm whales take roughly the same amount of biomass from the oceans as humans), and many other attributes (Whitehead 2003). The commercial value of the animal (a function of its size and the quality of Sperm Whale oil) drove two massive worldwide hunts: the technologically primitive “open-boat” hunt from 1712-~1920 (Starbuck 1878; Best 1983), and modern whaling using engine-driven whaling ships and harpoon guns from ~1910-1988 (Tonnessen and Johnsen 1982). The complex social structure of sperm whales may have been affected by whaling, lowering potential population growth rates, which are very low anyway (Whitehead 2003). On the positive side, Sperm Whales are very widely distributed (see above), and their primary prey, deep-water squid, are not yet major targets of fisheries.

The generation time (mean age of mothers) for Sperm Whales can be calculated if one assumes a set of population parameters, specifically age at first birth, mortality rate of mature females, and reproductive rate of mature females. There is uncertainty about these parameters, so two calculations were made using different assumptions:

a) Applying the population parameters most recently used for Sperm Whales by the International Whaling Commission’s Scientific Committee (International Whaling Commission 1982): age at first birth = 10 years; female reproductive rate in unexploited population = 0.20/year; female adult mortality = 0.055/yr): generation time = 27.3 years.

b) The estimates of mortality used by the International Whaling Commission are particularly problematic, and Sperm Whales likely have age-specific survival and reproductive rates. Thus it may be more realistic (Whitehead 2002) to use the well-established mortality schedule of Killer Whales (Orcinus orca; Olesiuk et al. 1990) and an age-specific pregnancy rate taken from the sperm whale data presented by Best et al. (1984; pregnancy rate for mature females = 0.257-0.0038xAge in years): generation time = 27.5

The greatest threat to Sperm Whales, extensive commercial whaling, has ceased. However, a number of other threats of various dimensions remain.

Sperm Whales have had a long history of local whaling going back at least to the 1500s and intense commercial whaling beginning around 1712 and continuing to 1988. The “modern” highly mechanised phase was particularly intense around 1950, and at its peak killed around 25,000 whales per year, dramatically depleting the global population. In recent decades, some tens of whales were taken each year from small boats in Indonesia (Reeves 2002), although none have been taken in the last two years (H. Whitehead pers. comm.), and 10 are taken annually by Japan under IWC Special Permit (Clapham et al. 2003).

Entanglement in fishing gear, particularly gillnets, has been a particular problem in the Mediterranean Sea (Reeves and Notarbartolo di Sciara, 2006), but Sperm Whales die from entanglement in nets and lines in many other areas and in a variety of fisheries as well (e.g., Haase and Félix 1994; Barlow and Cameron 2003). Considering the widespread distribution of Sperm Whales, observations of occasional takes in relatively small scale gillnet fisheries (e.g. Barlow and Cameron 2003) suggest much larger takes in unobserved, unregulated high seas driftnet fisheries such as were common before the 1989 adoption of resolution 44/225 of the UN General Assembly.

Sperm Whales sometimes take fish off fishing gear (most often demersal long-line gear), an activity known as “depredation.” Depredation of long-line catches appears to be a recent and increasing phenomenon, and now occurs in many regions (e.g., South East Alaska, Chile, South Georgia and several other southern ocean island areas, North Atlantic). This interaction has resulted in a few reported entanglements and deaths (e.g. Salas 1987; Hucke-Gaete et al. 2004), and has incurred hostility from some fishermen (National Marine Fisheries Service 1998; Donoghue et al. 2003), including shooting of whales (González and Olivarría 2002).

Sperm Whale tissues have high levels of some contaminants (O'Shea 1999; Nielsen et al. 2000); however, any population-level effects on health are unknown. The effects of noise on Sperm Whales are also uncertain. Some evidence suggests that they are highly sensitive to noise (e.g., Watkins et al. 1985; Bowles et al. 1994) while other studies have found little or no effect (e.g., Madsen and Møhl 2000; Madsen et al. 2002). To date, all published studies of Sperm Whales and noise focus on short-term behavioural effects. Avoidance of sonar (Dawson pers. comm.) and seismic surveys (Mate et al. 1994; but see Madsen et al. 2002) has been observed but no mortality has been documented.

Whaling on Sperm Whales has at various times focussed almost exclusively on one sex or the other. Removals of large numbers of males may have had lingering effects on pregnancy rates in some subpopulations (Best 1979; Clarke et al. 1980; Whitehead et al. 1997) and large males are noticeably uncommon on some breeding grounds (Whitehead 2003). The removal of large numbers of females from social groups, and of older females in particular, may have lingering, socially disruptive effects. Furthermore, recovery might be inhibited via temporary or permanent loss of social cohesion and of socio-ecological knowledge such as is known to occur in other large-brained, long-lived social mammals (e.g., elephants, Poole and Thomsen 1989).

Maximum rates of increase for Sperm Whale populations are very low, possibly on the order of 1% per year (Whitehead 2002). Population growth/recovery can be expected to be low in the species.

Sperm Whales face other threats at a more regional level. These include collisions with ships (Laist et al. 2001), for instance off the Canary Islands (André and Potter 2000) and in the Mediterranean (Pesante et al. 2002), and ingestion of marine debris in the Mediterranean (e.g., Viale et al. 1992).

Causes for optimism: On the one hand, the Sperm Whale is not being heavily whaled at present and seems relatively secure from this threat in the short and medium term. When not being actively hunted, the Sperm Whale has rather little interaction with humans: most of its habitat is far from land, and few of its food sources (principally deep-water squid) are of currently harvested (Clarke 1977). Some populations, for instance the animals in the western North Atlantic that were little affected by modern whaling, seem healthy with reasonably high population densities and evidence of satisfactory reproduction (Gordon et al. 1998; National Marine Fisheries Service 2000).

Causes for concern: on the other hand, the Sperm Whale, with a maximum rate of increase of around 1% per year (Whitehead 2002), is not well adapted to recover from population depletion. Furthermore, the population model considers only one anthropogenic threat, whaling, and thus posits that the Sperm Whale population has recovered since about 1980 (Fig. 1 in linked PDF document), when large-scale commercial whaling was rapidly coming to an end. This recovery is purely theoretical, and may not be occurring as sperm whales carry high levels of some chemical contaminants (O'Shea 1999; Nielsen et al. 2000), ocean noise is increasing (Gordon and Moscrop 1996), interactions with fisheries continue to result in sperm whale deaths (International Whaling Commission 1994), and the lingering, socially disruptive effects of whaling may be inhibiting recovery of this highly social species (Whitehead et al. 1997). Some regional populations of sperm whales are declining or are apparently not recovering from depletion. Even in the absence of whaling, the Mediterranean population appears to have declined over the past 20 years, with bycatch in driftnets a likely principal cause (Reeves and Notarbartolo di Sciara 2006). The southeastern Pacific Sperm Whale population, very heavily whaled during the period 1950-1980, has an extremely low recruitment rate (probably below replacement), perhaps because of the social disruption caused by intense whaling (Whitehead et al. 1997). The population of mature and maturing males in the Antarctic was also heavily whaled over the same period, but should have repopulated from less heavily exploited breeding populations at lower latitudes following the end of large-scale commercial whaling. However, systematic surveys of Sperm Whales in the Antarctic showed no substantial or statistically significant increase between 1978 and 1992 (Branch and Butterworth 2001).

Management plans need both development and implementation. The International Whaling Commission manages sperm whale populations under the International Convention for the Regulation of Whaling, and Schedule of the Convention lists Sperm Whale seasons, Sperm Whale size limits and Sperm Whale catch limits (0 at present), as well as sanctuaries for all species in the Indian and Southern Oceans. However, no scheme for managing Sperm Whale populations is in place. Moreover, many range states are not members of the International Whaling Commission.

Regional subpopulations of Sperm Whales exist, and there has been an apparent lack of recovery in some areas or even continued decline (e.g., the Mediterranean (Reeves and Notarbartolo di Sciara 2006). Therefore, further assessments of the status of Sperm Whales should be conducted at the subpopulation level.

In-Place Research, Monitoring and PlanningIn-Place Land/Water Protection and Management Conservation sites identified:Yes, over entire rangeIn-Place Species ManagementIn-Place Education Included in international legislation:Yes Subject to any international management/trade controls:Yes

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Clarke, R., Aguayo, A. and Paliza, O. 1980. Pregnancy rates of sperm whales in the southeast Pacific between 1959 and 1962 and a comparison with those from Paita, Peru, between 1975 and 1977. Reports of the International Whaling Commission, Special Issue 2: 151-158.

Fujino, K. 1963. Identification of breeding subpopulations of the sperm whales in the waters adjacent to Japan and around Aleutian islands by means of blood typing investigations. Bulletin of the Japanese Society of Scientific Fisheries 29: 1057-1063.

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Haase, B. and Felix, F. 1994. A note on the incidental mortality of sperm whales (Physeter macrocephalus) in Ecuador. Reports of the International Whaling Commission Special Issue 15: 481-484.

Olesiuk, P., Bigg, M. A. and Ellis, G. M. 1990. Life history and population dynamics of resident killer whales (Orcinus orca) in the coastal waters of British Columbia and Washington State. Reports of the International Whaling Commission 12: 209-243.